This invention relates to dynamoelectric machines and more particularly to improvements in spindle motors for disc drives.
It is common in three-phase spindle motors to have nine coil armatures (stators) connected in three discrete phases and eight pole permanent magnet rotors specifically arranged to minimize cogging torque and torque ripple. Examples of such motors are disclosed in Konecny U.S. Pat. No. 4,774,428 and Crapo U.S. Pat. No. 4,847,712. These utilize various winding patterns for realizing the stated advantages; however, they all require that all poles on the stator have coils; i.e., each pole have a coil such that a nine-pole stator has nine coils. In order to obtain opposite polarities on adjacent poles within a single phase, it has been necessary to wind the coils oppositely. Hence, the resulting structure has one coil for each pole (nine coils for nine poles) with adjacent coils being wound oppositely requiring at least two separate winding operations. Two-phase motors having auxiliary salient poles between wound poles are known, however.